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Cape Hatteras, NC 2

 What is the force that drives the ocean’s currents? What is the basic pattern of surface currents?  How do surface ocean currents influence climate?  What is thermohaline circulation?  Why is the shoreline considered to be a dynamic interface?  What factors influence the height, length and period of a wave? Can you describe the motion of water within a wave? 3

 How do waves erode?  What are some typical features produced by wave erosion and from sediment deposited by beach drift and longshore currents?  What are the local factors that influence shoreline erosion, and what are some basic responses to shoreline erosion problems?  How do emergent and submergent coasts differ in their formation and characteristic features?  How are tides produced? 4

 Surface circulation  Ocean currents are masses of water that flow from one place to another  Surface currents develop from friction between the ocean and the wind that blows across the surface  Huge, slowly moving gyres 5

 Surface circulation  Five main gyres North Pacific Gyre South Pacific Gyre North Atlantic Gyre South Atlantic Gyre Indian Ocean Gyre (mostly S. Hemisphere)  Related to atmospheric circulation Trade winds, westerlies Also influenced by major landmasses 6

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 Surface circulation  Deflected by the Coriolis effect To the right in the Northern Hemisphere To the left in the Southern Hemisphere  Four main currents generally exist within each gyre ~6 years to make the loop in Pacific (Box 15.1)  Large central zone w/no well-defined currents  West Wind Drift is the only one that completely circles the Earth 8

 Surface circulation  Importance of surface currents Climate Currents from low latitudes into higher latitudes (warm currents) transfer heat from warmer to cooler areas As N. Atlantic Current approaches W. Europe, kit splits; part of it carries warm air to Great Britain, Norway, Iceland Canary Current - travels south (cool) 9

10 A)On a non-rotating Earth, rocket would travel straight to its target. B)Earth rotates 15  /hr so even though rocket travels in a straight line, it follows a curved line that veers to the right of the target.

11 A)~1769: Benjamin Franklin’s Gulf Stream chart B)Satellite image of Gulf Stream (warm – orange)

 Surface circulation  Importance of surface currents Climate Influence of cold currents is most pronounced in the tropics or during the summer months in the middle latitudes Cold currents travel  equator, moderate climate Aridity quite pronounced in w. South America, Africa  Lower atmosphere chilled by cold offshore water  Air is more stable, less likely to move upward and form rain clouds 12

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 Surface circulation  Importance of surface currents Upwelling The rising of cold water from deeper layers Most characteristic along west coasts of continents Coastal winds + Coriolis Effect  surface water moves away from shore Brings greater concentrations of dissolved nutrients to the ocean surface 15

Coastal upwelling  high photosynthesis

 Deep-ocean circulation  Significant vertical movement (surface circulation is mostly horizontal)  A response to density differences  Factors creating a dense mass of water Temperature – cold water is dense Salinity – density increases with increasing salinity  Called thermohaline circulation 17

18 When seawater freezes, salt doesn’t become part of ice; water becomes denser and sinks

 Deep-ocean circulation  Most water involved in deep-ocean currents begins in high latitudes at the surface  A simplified model of ocean circulation is similar to a conveyor belt that travels from the Atlantic Ocean, through the Indian and Pacific Oceans and back again  Warm water in ocean’s upper layers flows poleward Becomes dense and sinks Returns to equator as cold, deep water Eventual upwelling 19

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 The land-sea boundary (interface)  Dynamic – topography, geology, climate vary greatly  Shoreline – contact between land and sea  Shore – area between lowest tidal level and highest areas affected by storm waves  Coastline – the seaward edge of the coast  Beach – accumulation of sediment along the landward margin of the ocean 21

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Crystal Beach TX (9/16/08), 3 days after Hurricane Ike. Most of the damage was caused by a storm surge. MAPMAP

Sanibel Island, FL: beach is made of shells, shell fragments

Hawaii: beach is derived from dark volcanic rock

26 Green Sand Beach at Puu Mahana, Hawaii: green material is olivine sand ((Mg,Fe) 2 SiO 4 ); dark gray material is basalt lithic sand.

27 Gulf St. Vincent, southern Australia: all quartz (SiO 2 )

28 Basalt cobble beach at Yaquina Head, coastal Oregon, 8/3/12

 Waves  Energy traveling along the interface between ocean and atmosphere  Can transfer energy 1000s of km  Derive their energy and motion from wind  Shape/modify shorelines that must absorb energy  Parts Crest Trough 29

 Waves  Measurements of a wave Wave height – the distance between a trough and a crest Wavelength – the horizontal distance between successive crests (or troughs) Wave period – the time interval for one full wave to pass a fixed position 30

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 Waves  Wave height, length, and period depend on Wind speed Length of time the wind blows Fetch – the distance that the wind travels  As the wave travels, the water passes energy along by moving in a circle Waveform moves forward At a depth of about one-half the wavelength, the movement of water particles becomes negligible (the wave base) 32

 Waves  Swells – waves that have traveled away from area of origination Sea waves seen from shore are usually a mix of swells from faraway storms and waves created by local winds 33

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35 Pier Camera

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 Wave erosion  Caused by Wave impact and pressure Breaks down rock material and supplies sand to beaches Abrasion – sawing and grinding action of water armed with rock fragments 40

 Beaches are composed of whatever material is available  Some beaches have a significant biological component  Material does not stay in one place Wave energy moves large quantities of sand parallel and perpendicular to the shoreline 41

 Wave refraction  Bending of a wave  Wave arrives parallel to shore  Results Wave energy is concentrated against the sides and ends of headland Wave erosion straightens an irregular shoreline 42

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 Longshore transport  Beach drift – sediment moves in a zigzag pattern along the beach face  Longshore current Current in surf zone Flows parallel to the shore Moves substantially more sediment than beach drift 44

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 Erosional features  Wave-cut cliff  Wave-cut platform  Marine terraces  Associated with headlands Sea arch Sea stack 46

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 Depositional features  Spit – a ridge of sand extending from the land into the mouth of an adjacent bay with an end that often hooks landward  Baymouth bar – a sand bar that completely crosses a bay  Tombolo – a ridge of sand that connects an island to the mainland 49

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 Depositional features  Barrier islands Mainly along the Atlantic and Gulf Coastal Plains Parallel the coast Originate in several ways 53

 Shoreline erosion is influenced by the local factors  Proximity to sediment-laden rivers  Degree of tectonic activity  Topography and composition of the land  Prevailing wind and weather patterns  Configuration of the coastline 54

 Responses to erosion problems  Hard stabilization – building structures Types of structures Groins – barriers built at a right angle to the beach that are designed to trap sand Breakwaters – barriers built offshore and parallel to the coast to protect boats from breaking waves Seawalls – Armors the coast against the force of breaking waves Often these structures are not effective 55

 Responses to erosion problems  Alternatives to hard stabilization Beach nourishment by adding sand to the beach system Relocating buildings away from beach  Erosion problems along U.S. Coasts  Shoreline erosion problems are different along the opposite coasts 56

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 Erosion problems along U.S. Coasts  Atlantic and Gulf Coasts Development occurs mainly on barrier islands Face open ocean Receive full force of storms Development has taken place more rapidly than our understanding of barrier island dynamics 59

 Erosion problems along U.S. Coasts  Pacific Coast Characterized by relatively narrow beaches backed by steep cliffs and mountain ranges Major problem is the narrowing of the beaches Sediment for beaches is interrupted by dams and reservoirs Rapid erosion occurs along the beaches 60

Solana Beach to Del Mar, San Diego County, California 61

 Shoreline classification is difficult  Classification based on changes with respect to sea level  Emergent coast Caused by Uplift of the land, or A drop in sea level 62

 Classification based on changes with respect to sea level  Emergent coast Features of an emergent coast Wave-cut cliffs Marine terraces 63

 Classification based on changes with respect to sea level  Submergent coast Caused by Land adjacent to sea subsides, or Sea level rises Features of a submergent coast Highly irregular shoreline Estuaries – drowned river mouths 64

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 Changes in elevation of the ocean surface  Caused by the gravitational forces exerted upon Earth by the  Moon, and to a lesser extent by the  Sun 66

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 Monthly tidal cycle  Spring tide During new and full moons Gravitational forces added together Especially high and low tides Large daily tidal range 68

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 Monthly tidal cycle  Neap tide First and third quarters of the Moon Gravitational forces are offset Daily tidal range is least  Tidal patterns  Many factors influence the tides Shape of the coastline Configuration of the ocean basin Water depth 71

 Tidal patterns  Main tidal patterns Diurnal tidal pattern A single high and low tide each tidal day Occurs along the northern shore of the Gulf of Mexico Semidiurnal tidal pattern Two high and two low tides each tidal day Little difference in the high and low water heights Common along the Atlantic Coast of the United States 72

 Tidal patterns  Main tidal patterns Mixed tidal pattern Two high and two low waters each day Large inequality in high water heights, low water heights, or both Prevalent along the Pacific Coast of the United States 73

 Tidal patterns  Tidal currents Horizontal flow accompanying the rise and fall of tides Types of tidal currents Flood current – advances into the coastal zone Ebb current – seaward moving water Sometimes tidal deltas are created by tidal currents 74

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Break the Grip of the Rip 76

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